Compared with a double-dimension (2D) display device, a three-dimension (3D) display device usually needs a specific grating layer installed additionally. Methods for realizing a grating layer of the current mainstream 3D display device are mainly divided into two types: a parallax barrier method and a lens-grating method.
The basic principle of the parallax barrier method is as shown in FIG. 1. A left-viewing-field pixel 11 of a display panel 1 displays a left-eye image, while a right-viewing-field pixel 12 displays a right-eye image. A parallax barrier 13, as a grating layer, is placed in front of the display panel 1, and the parallax barrier 13 is composed of light-shielding stripes and light-transmissive stripes, which are alternated. The light-shielding stripes of the parallax barrier 13 block light from a right-eye image for a viewer's left eye, and block light emitted from a left-eye image for the viewer's right eye. The viewer separately watches different images with his left and right eyes, and eventually combines the images to obtain a stereo perception. The distance between a typical viewer's two eyes is an interpupillary distance T of human, which is about 60 mm. As an example, for a general display device, the width of a pixel is P=60 μm, and the viewing distance is set to L=300 mm; then, with reference to FIG. 1, the distance H between the parallax barrier and a light-emitting point of the display panel can be roughly calculated with the following expression:
                    H        =                              L            *            P                    T                                    (                  Expression          ⁢                                          ⁢          1                )            
As can be seen, under normal circumstances, the distance H between the parallax barrier and a light-emitting point of the display unit needs to be 0.3 mm or so. In order to ensure that the distance H between the parallax barrier and a light-emitting point of the display unit reaches this height, usually an layer of parallax barrier is required to be additionally provided on the display device which has been formed by a cell-assembling process after the display device is manufactured. Thus, on the basis of the existing production method, a new process has to be added or new production equipments have to be employed, which will result in an increase of the production costs of a 3D display device.
The lens-grating method refers to that a lenticular lens is placed in front of a display panel and functions as a grating layer; the left-viewing-field sub-pixels on the display panel display a left-eye image, and the right-viewing-field sub-pixels display a right-eye image; the light emitted from the pixels of the left- and right-viewing-fields is deflected in its propagation direction when passing through the lenticular lens grating due to the refraction effect of the lenticular lens grating, so that the light from the left-viewing-field pixels is incident into the left eye of a viewer, and the light from the right-viewing-field pixels is incident into the right eye of the viewer, which both are finally used to produce a 3D effect. FIG. 2 is a simplified structure of a lenticular lens grating 3D display. A light-emitting point of the display unit is located in the focal plane of the lenticular lens, and the focal length is denoted as f. The distance from the lower surface of the lenticular lens to a light-emitting point of the display unit is denoted as H, and here f=H. The width of each pixel of the viewing-fields is denoted as P, and the pitch of the grating is approximately equal to 2P. The refractive index of the lens is denoted as n2, and the refractive index outside of the lens is denoted as n1. The radius of the lens is denoted as r, and the arch-height of the lens is denoted as g. Thus, there is an expression as follows:
                              g          -          r                =                                                            n                ⁢                                                                  ⁢                1                                            n                ⁢                                                                  ⁢                2                                      *                                                            H                  2                                +                                  P                  2                                                              -          H                                    Expression        ⁢                                  ⁢        2            
The arch-height g of a lens is an important parameter. The width P of each pixel of the viewing-fields is about 60 μm; n2 is the refractive index of a common resin, which is about 1.5; n1 is the refractive index of air, which is 1; generally H is the thickness of an upper glass substrate, which is about 0.5 mm; the radius of a lens is r, and for a perfect lens, r=f(n2−1). With the expression 2, it can be calculated that, in the existing structure, the arch-height g of a lens is at least more than 11 μm. It is meant that, the higher the arch-height of the lens is, the larger the thickness of the lens-grating layer is; however, a lens-grating layer having a relatively large thickness is difficult to be manufactured with the existing patterning processes. In order to accord with changes in product specifications, a new process has to be added or new production equipments have to be employed on the basis of the existing production method, which will result in an increase of the production costs of a 3D display device.
As can be seen, it is difficult for the existing 3D display device to solve such problem that, the production costs are increased in the manufacturing processes of a grating layer, because a parallax barrier is required to be additionally attached on the display device which has been formed by a cell-assembling process, or because the arch-height of the lens needs to be increased.